Good evening, tonight, we investigate an internet real estate scam that is sweeping the nation. Incredible deals on beautiful houses for that perfect getaway. But there is just one little detail the listing is leaving out. The actual homeowners have no idea what is going on. So we went undercover to get to the bottom of it for our series, nightline on the lookout. Ryan and I are standing here at the rental hall. Reporter: This, ladies and gentlemen, is a stick-up. David? No gun or getaway car required. Anyone here? Reporter: All the bad guys here needed was an internet connection and some stolen photos. You wouldn't have taken our money, would you? They almost got bribed. A regular guy from indiana who read the ad to rent the house behind us. But ryan is helping us lay a trap now, for a man who took nearly $2,000, promised to meet us with a key and never showed up. Leave a message after the tone. Reporter: All over the country, people are losing money to fake rental listings. More than ever before, according to the fbi. Even in this small oregon town, 15 separate victims lost more than $20,000 on the exact same house. Advertised on craigslist, by a shadowy fake landlord. And here in california. I should have thought wow, you know, $400 a night, this house is amazing. How could that be? And I thought maybe we were lucky. Reporter: Sherry mccaffrey booked this house in south lake tahoe for her extended family, all 14 of them, through the rental website. Her cousin, joyce, along with her husband and daughter, got there first, while sherry was still on the road they walk right in. It is sprawling, a big place. It will be decked out. I feel like singing, so happy. Reporter: There was just one problem. So I came home recently, and much to my surprise there was a car here in my driveway. Reporter: The owner had not put his home up for rent. And I could see there were people milling around in my house, I took a picture of the slats here and recognized there were total strangers entering my house. I entered my house, worried. All of a sudden we saw a man come in. The little girl sort of screamed. I informed them that I was the owner of the house. He basically said, sorry to tell you this, but you guys have been scammed. Reporter: But the mccaffrey family were not the only ones to arrive on shawn's door step. Over the last two weeks, i have confirmed episodes with families, groups, believing they rented their house. They have been scammed. Reporter: Less than one in 10,000 listings are fake. But they confirm there were ten other travellers who thought they had rented shawn's house through the listings seen on their website. Authorities are still looking for the cyber criminal who did it. According to the fbi, the people who create these ads are virtually impossible to catch. You don't have to be a bugsy siegel with a machine gun anymore. Really what you have to do is be a guy with access to the internet if you want to scam people out of their money. A faceless transaction, and crooked people take advantage of that and exploit people. Reporter: We wanted to flush out one of these phantom landlords by posing as an unsuspecting target. So that is how we got involved with brian. He found his dream rental on craigslist, a sprawling house on the island of nantucket, for $1500 a week. This house in the ad looked just fantastic. Reporter: Ryan and his wife planned an end of summer vacation before two of their kids left for college. But then, he got suspicious. The more I looked at the house I was getting more concerned that it really was too good to be true. Reporter: So ryan pulled a nancy drew. He called the nantucket hall and tracked down the owner of the house he wanted to rent. So at that point, I had the name, the address of somebody in new york, the real owner of the property. Reporter: It won't surprise you his name was not david. He had no clue his house was on craigslist, he was renting the house, but not for 2,000 a week, try $20,000. I think they took the pictures of the house from the internet, and created their own craigslist ad. And that was it. Reporter: It is called scraping. Creating fraudulent rental listings by using photos, details and descriptions, scraped from other legitimate websites. In this case, probably from when the house was on the market a year ago. But it was not the image that first raised brian's suspicions. It was the poor grammar in david's texts and e-mails. He handed them over to us. After weeks of texting back and forth we get david on the phone. I pose as ryan's wife to arrange payment and go over the details of arrival. We're so excited about our vacation. David promises to meet us with the keys in front of the house. Sorry, I didn't hear you well. But the phone connection is horrible. Something to look out for. If you think you're talking to somebody in nigeria, you just might be. So when we get off the ferry, do we go left or right? And while I know something about the geography of nantucket island, I'm beginning to get the hunch that david doesn't. In the following week, we travel to nantucket, meet up with ryan to see if david will actually show up. What do I do, turn left? I would turn right. Reporter: After trying to follow his directions. Here we go, here is the right. My suspicion was confirmed. Found a light house, but not the house. Okay. So we put the address in our gps. It's beautiful. Which house is that. So we're looking for. Reporter: We arrive at the actual house where we wait. And wait, and wait. David? Ryan and I are standing here at the rental house but you're supposed to be here with the key and it is 12:09. Reporter: All we got was his voice mail, but there was one last lead on the bottom of the fake rental contract. We noticed there was a fake address for david's supposed company. And you're not a real estate agent? No. Reporter: David's trail has gone cold. And we're pretty sure he is gone for good. There is not very much to do about it. Reporter: It is a story we found out local police are all too familiar with. Do you have the resources to fix this? Locally we don't. Generally we refer the cases to different federal agencies, the fbi, the secret service or the postal inspectors, with varying degrees of success. Reporter: Frankly, it is just too small for them. And how much do you have to have lost to be able for the fbi to step in? Typically, a million dollars or more, it is part of an organized crime ring. Reporter: So unless you're renting the entire nantucket island, it is ultimately up to you to protect yourself from people like david. We had some unfinished business and were determined to confront david about ripping us off. Just a couple of days ago we reached david on the phone. Hi, david? He is still at it. This time, he is trying to rent us an apartment in new york. We sent you 1850 bucks, to rent a house in nantucket. You were supposed to meet us with the key but you never came. How many people have you ripped off? How many people have you stolen money from? Expletive. He said he is not a criminal, he says he is in brooklyn. I don't think so. Ryan's family didn't end up with their dream house, but still had a dreamy vacation. AND SO DID the McCaffrey clan in lake tahoe, who found a great vacation. Never let them book your vacation. Well, the website tells us they are actively collecting data about these crimes, and if you have been taken, providing details to the fbi may ultimately help them catch the crooks. For more information visit our website at abcnews.Com/night line.

This transcript has been automatically generated and may not be 100% accurate.

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